Previously purified derivatives of acrylamido sulfonic acid monomers are prepared utilizing the already purified sulfonic acid.
U.S. Pat. No. 4,337,215 (Doi et al, Jun. 29, 1982) relates to a purification process for the efficient preparation of high-purity 2-acrylamido-2-methylpropanesulfonic acid (hereinafter referred to simply as AMPS monomer, a registered trademark of The Lubrizol Corporation). In this process, the starting material is crude AMPS monomer crystals which have been obtained by washing precipitates from the reaction mixture obtained by any of the conventional reaction methods. The crude crystals are dissolved in hydrous acetic acid containing 5 to 40% water. The quantity of the hydrous acetic acid required to completely dissolve the desired amount of AMPS monomer at 90.degree. C. depends on the water content. When the hydrous acetic acid has a water content of 10%, it is used in an amount about 4 to 5 times the weight of crude crystals. The purified crystals are collected by filtration of this solution after the solution is cooled to about 10 to 20.degree. C.
U.S. Pat. No. 4,701,283 (Itoh et al, Oct. 20, 1987) relates to a process for preparing amidoalkanesulfonic acids and derivatives, such as salts thereof, as well as copolymer-coated solid materials, copolymer emulsions and pigment dispersants in which the copolymer is obtained by copolymerizing such an amidoalkanesulfonic acid derivative with another monomer.
U.S. Pat. No. 4,650,614 (Jevne et al, Mar. 17, 1987) provides a method for purifying reaction grade 2-acrylamido-2-methylpropanesulfonic acid, as obtained commercially, by a short duration, mild heating of the acid in a slurry with a volatile liquid monohydric alcohol followed by acid recovery via decantation or other form of separation and subsequent drying of the wet solid acid.